Absorbent tissue products such as paper towels, facial tissues, bath tissues and other similar products are designed to include several important properties. For example, the products should have good bulk, a soft feel and should be highly absorbent. The product should also have good strength and resist tearing, even while wet. Unfortunately, it is very difficult to produce a high strength tissue product that is also soft and highly absorbent. Usually, when steps are taken to increase one property of the product, other characteristics of the product are adversely affected.
For instance, softness is typically increased by decreasing or reducing cellulosic fiber bonding within the tissue product. Inhibiting or reducing fiber bonding, however, adversely affects the strength of the tissue web.
In other embodiments, softness is enhanced by the topical addition of a softening agent to the outer surfaces of the tissue web. The softening agent may comprise, for instance, a silicone. The silicone may be applied to the web by printing, coating or spraying. Although silicones make the tissue webs feel softer, silicones can be relatively expensive and may lower sheet durability as measured by tensile strength and/or tensile energy absorbed.
In order to improve durability, in the past, various strength agents have been added to tissue products. The strength agents may be added to increase the dry strength of the tissue web or the wet strength of the tissue web. Some strength agents are considered temporary, since they only maintain wet strength in the tissue for a specific length of time. Temporary wet strength agents, for instance, may add strength to bath tissues during use while not preventing the bath tissues from disintegrating when dropped in a commode and flushed into a sewer line or septic tank.
Bonding agents have also been topically applied to tissue products alone or in combination with creping operations. For example, one particular process that has proved to be very successful in producing paper towels and wipers is disclosed in U.S. Pat. No. 3,879,257 to Gentile. et al., which is incorporated herein by reference in its entirety. In Gentile, et al., a process is disclosed in which a bonding material is applied in a fine, defined pattern to one side of a fibrous web. The web is then adhered to a heated creping surface and creped from the surface. A bonding material is applied to the opposite side of the web and the web is similarly creped. The process disclosed in Gentile. et al. produces wiper products having exceptional bulk, outstanding softness and good absorbency. The surface regions of the web also provide excellent strength, abrasion resistance, and wipe-dry properties.
Although the process and products disclosed in Gentile, et al. have provided many advances in the art of making paper wiping products, further improvements in various aspects of paper wiping products remain desired. For example, particular strength agents are still needed that can be incorporated into tissue webs without significantly adversely impacting the softness of the webs. A need also exists for a strength agent that can be incorporated into the web at any point during its production. For instance, a need exists for a strength agent that can be added to a pulpsheet prior to slurry formation, an aqueous suspension of fibers used to form a tissue web, a formed tissue web prior to drying, and/or to a tissue web that has been dried.
Furthermore, in the past, additive compositions topically applied to tissue webs had a tendency, under some circumstances, to create blocking problems, which refers to the tendency of two adjacent tissue sheets to stick together. As such, a need also exists for an additive composition or strength agent that is topically applied to a tissue web without creating blocking problems.